Erectile dysfunction (ED) is a highly prevalent condition estimated to affect 10-20 million men in the US. There is a substantial body of evidence linking ED and cardiovascular disease (CVD), implying a common underlying vascular disease. As progressive loss of vasodilation manifests sooner in the vasculature of the erectile system than in systemic conduit vessels, an important implication for public health is that ED may act as a warning signal for impending CVD. Recent finding from the Massachusetts Male Aging Study have shown remission of ED symptoms to be more common then previously thought with up to one-third of men with ED reporting spontaneous remission. Endothelial dysfunction, characterized by loss of nitric oxide (NO), is the biologic mechanism underlying ED and CVD and has been shown to precede atherosclerosis. However, longitudinal data on the impact of endothelial dysfunction on the incidence, progression, and remission of ED are lacking, and thus the role of ED in preventive interventions for heart disease remains inconclusive. The goal of the proposed research is to provide the first systematic investigation of the prospective relationship between endothelial dysfunction and ED in a large population-base sample of men. The proposed study is an ancillary study of the Boston Area Community Health (BACH) survey, an epidemiologic study of a broad range of urologic symptoms, that includes a cohort of 2,301 race/ethnically diverse men age 30-79 at baseline. Participants in the proposed study will be recruited from the BACH/Bone cohort, an ancillary study of BACH on musculoskeletal health in a randomly selected group of 1,219 black, Hispanic, and white BACH men. Endothelial function will be measured in 400 men using forearm brachial artery flow mediated dilation (FMD), a measure commonly used to assess endothelial dysfunction. A baseline assessment will be followed up at 2 years with the same measurements. The present study will cost-efficiently draw on the wealth of background demographic, biomedical and psychosocial data on the well-characterized cohort of the parent BACH study and its ancillary study, BACH/Bone. Public Health Relevance: Cardiovascular disease is the most important cause of premature death in the adult population of the U.S. and erectile dysfunction may be an early indicator of vascular disease that could be clinically useful for identification of higher risk men as candidates for interventions to reduce risk of future cardiovascular events. As there are no existing studies of longitudinal assessments of both erectile dysfunction and endothelial dysfunction, the proposed study is likely to provide new information in this area.